There are many localization algorithms which can be divided into range-based localization algorithms and range-free localization algorithms according to whether there is a need to measure the distances of actual nodes in a positioning process. The range-based localization scheme is a method to estimate the positions of the nodes by measuring the distance or angle information between the nodes through the triangle and centroid location algorithm, a trilateration localization method, a least square method or a maximum likelihood estimation, etc. The existing common ranging technology includes TOA (time of arrival), TDOA (time difference of arrival), AOA (angel of arrival) and RSSI (Received Signal Strength Indication), etc. The range-free localization algorithm is a method to complete the estimation of the positions of the nodes without measuring the distance or angle information between the nodes only according to the information of network connectivity, etc. The common method includes: a centroid localization algorithm, an Amorphous algorithm, a DV-Hop algorithm, an APIT algorithm, etc. Compared with such range-based localization algorithms as TOA, TDOA, AOA, etc., the trilateration localization method based on RSSI does not need additional hardware overhead and has the advantages of low realization complexity, low hardware resource overhead, etc.
With the continuous development of informationization technology, people's need for positioning and navigation technologies is increasingly grown. The wireless range-based localization method has a significant status in the positioning technology and plays an increasing pole in the fields of military affairs, sailing, etc. Wherein, the ranging based on Received Signal Strength Indication (RSSI)—and the trilateration localization method are representative realization solutions. RSSI is used to estimate the distance between two communication nodes through received signal strength so as to realize positioning. Because its positioning principle is simple and RSSI values can be obtained to realize positioning without additional hardware overhead, RSSI is becoming a research hotspot of the wireless positioning technology. However, the ranging error is large because the RSSI values are affected by the multipath effect in actual ranging, resulting in an influence on the position accuracy. The trilateration localization method is constrained by the ranging accuracy, so the precision of the position coordinate is further affected. Thus, it is necessary and meaningful to research how to increase the RSSI ranging positioning accuracy and improve the positioning algorithm.
At present, there are two major aspects about the research of RSSI ranging precision. One aspect is to use the RSSI value of a single channel given by communication chips to conduct a large number of actual environmental tests and to conduct averaging, Gaussian model fitting, differential operation, etc. according to a fading channel model to reduce the ranging error. The other aspect is to give an improvement on the RSSI algorithm. Some reduce transient interference and noise interference by screening strange signals through FIR and ITR filtering, some propose an algorithm for weighting the RSSI value and some introduce the maximum likelihood estimation into the positioning of the “constant-logarithm” model. However, these methods fail to consider the influence of the multipath effect.
Because increasing wireless technologies use ISM frequency band, it is very easy to suffer co-channel interference for communication in this frequency band.
As a result, it is urgent to provide a method for reducing co-channel interference, obstacle blocking and multipath effect response with respect to the problem of—positioning precision based on RSSI.
The frequency-hopping spread spectrum (FHSS) technology is a novel wireless technology that appears in recent years. It builds on multi-channel communication and prevents random interference and multipath effect from affecting communication reliability by continuously changing the channels. In the FHSS process, the channel through which each packet of two wireless devices is sent is different from the channel through which the previous packet is sent. Such technology is used earliest in the IEEE802.15.1 protocol (Bluetooth). In Bluetooth cluster, a device that wants to communicate with the head of the cluster shall be keep time synchronized with the head of the cluster first; and then, Hash algorithm is used to map the address of the head of the cluster into an FHSS sequence. All the nodes will comply with this FHSS sequence to switch the channels for 1600 times/minute. IEEE802.15.4 also uses the FHSS technology. In the 2.4 GHz frequency band, IEEE802.15.4 uses 16 channels to conduct FHSS and specifies that the switching time between the channels is less than 192 μs.